The study found that the MUAC and SBSF measures presented greater correlations with VAT and TAT during the first 20 weeks of pregnancy, with a higher correlation than the pre-pregnancy BMI value. It is important to emphasize that these anthropometric measurements are considered low cost, efficient and replicable in in under-resourced settings.
These findings are particularly valuable in cases where pregnancy discovered late or if the individual does not accurately remember their pre-gestational weight in clinical practice, making it difficult to correctly estimate pre-pregnancy BMI. Currently, pre-pregnancy BMI is the anthropometrical indicator of the nutritional state most used as a metabolic risk marker, because women who were overweight or obese are at an elevated relative risk of preeclampsia (17, 18), cesarean section delivery (17), gestational diabetes (18), increasing the relative risk of intrauterine death (18) and more likely to be macrosomic (17). However, this index is limited with regard to the differentiation of adipose content (1), particularly in the central region, the focus of the present study. Furthermore, despite the ease of measuring BMI, it has low predictive precision for abnormal pregnancy results; therefore, new diagnostic modalities can improve these scores, as demonstrated by Bourdages et al. (2018) and Souza et al. (2016), where the increase in visceral adipose tissue, identified during the first trimester, was associated with a greater chance of developing gestational diabetes mellitus (9, 19).
Research indicates that the use of circumferences and skinfolds to determine maternal nutritional state during the first weeks of pregnancy can facilitate metabolic risk detection (1, 7). A study made in Nigeria with 578 pregnant women showed that MUAC has a strong positive correlation with maternal weight and could be used to identify obesity in women regardless of stage of pregnancy. The authors found that MUAC values of 33cm might be reliable cut off points for diagnoses of obesity throughout pregnancy (15). Another study in Central Malaysia with 498 pregnant women found that MUAC was inversely associated with an inadequate rate of gestational weight gain, as compared to normal gestational weight gain (13). Besides that, a cross-sectional study conducted in South Africa with 164 women showed a strong correlation between MUAC and pre-pregnancy BMI in pregnant women up to 30 weeks' gestation. The authors found that the MUAC cut-offs for obesity and malnutrition were calculated as 30.57 cm and 22.8 cm, respectively (6).
Along with the use of MUAC to determine maternal metabolic risk, SBSF proved useful in detecting low weight newborns in a prospective study conducted in Argentina with 488 pregnant women. The authors found that a low increase of skinfolds during pregnancy can indicate low birthweight, demonstrating significant consequences to the offspring’s health (20, 21).
On the other hand, the measurement of the different compartments of abdominal fat via ultrasound provides an adequate estimate of central adiposity (22); however, the assessment of maternal central fat is not routinely performed in obstetric ultrasounds. The risk of adverse conditions caused by an excess of fat, particularly visceral fat, to the pregnant woman and fetus health is clearly consolidated in the literature (8, 10, 17, 23, 24), therefore, thus the precision and cost appraisal of different fat compartments is highly important to the population (25).
Aligned with the Brazilian Ministry of Health recommendations on resolute prenatal care (26) and the isolated capacity of MUAC and SBSF to detect the increase in amounts of maternal central fat, the inclusion of clinical anthropometry during the first 20 weeks of pregnancy can contribute to accurate maternal metabolic risk prediction. Thus, their complementary use in clinical practice is justified, as well as their possible inclusion in protocols for nutritional assessment during pregnancy. MUAC in particular can act as an alternative tool in screening for patients with metabolic risk in developing countries where monitoring of weight gain is not feasible due to limitations involving equipment (adipometer, for example), team or prenatal coverage.
It is well known that the early diagnosis of metabolic risk during the first half of pregnancy allows for the early implementation of preventive and therapeutic measures, resulting in improved maternal and fetal health due to immediate action following diagnosis (27). On the other hand, cases where the maternal central fat estimate is appropriate, according to the suggested anthropometry, even among obese women, the high cost of following patients without metabolic risk and high risk prenatal could be avoided.
Strengths and limitations
The study was conducted in a low risk primary healthcare setting that did not provide additional intervention to the sample. The data were obtained from routine follow-up of patients, which suggests that the findings can be easily transferred to the clinical practice. The most important aspect of the research was that the study’s population was comprised of pregnant women where the anthropometrical measurements can be become tools for decision making in clinical practice both in low and high obstetric risk environments. The low number of researchers involved in data collection minimizes possible mistakes of measurement. Throughout the study, one researcher was in charge of ultrasound collections and two researchers were in charge of the general questionnaire and nutritional assessment. A limitation of the study is the cross-sectional design that prevents the verification of pregnancy outcomes among women with large amounts of central fat due to the absence of blood sampling that diagnoses metabolic risk in pregnancy. Another limitation of the study includes the self-reporting of pre-pregnancy weight, as it may have been affected by recall bias. However, several studies demonstrated that the use of self-reported weight in pregnant women and young adults is valid (28, 29).